Well, I guess the title says it all. Leaf++ is the brain child of Italian artist Salvatore Iaconesi that couples together visual search and social networks to augment (you guessed it) leaves. A user can leave (no pun intended) a message on a leaf, to be seen later by other users scanning the same leaf type.
Watching the above video, it seems that some people get high on leaves.
More details can be found on Iaconesi’s site.